Hammer mill with equalized separating means



June 30, 1936. w LJ CLEMENT 2,045,582

HAMMER MILL WITH EQUALIZED SEPARATING MEANS Filed Fe 11, 1930 3 Sheets-Sheet 2 June 30, 1936. w. J. CLEMENT HAMMER MILL WITH EQUALIZED SEPARATING MEANS Filed Feb 11, 1930 3v Sheets-Sheet 3 I W422i M; 1m w w Patented June 30, 1936 UNITED STATES HAMMER. MILL wrrn aouauzan SEPARATING MEANS Walter J. Clement, New Hartford, N. Y., aasignor to Bossert Company, Inc., Utica, N. Y., a corporation of New York Application February 11,1930, Serial No. 421,531

3 Claims.

This invention relates primarily to grinding mills of the type in which a screen is used in connection with an induced flow of air to separate sufiiciently ground material from that which has not yet been reduced to a desired degree of fineness. More particularly it is concerned with means for distributing the suction efiect by which flow of air laden with the disintegrated material through the screen is obtained, to the end that this eflect may be equalized as nearly as possible throughout the area of the screen. The principles of the invention, however, are not necessarily limited to use only in connection with grinding mills, although such association is a feature of the invention and is claimed herein, but includes broadly the combination of pressure distributing or equalizing means with a screen for separating particles of different degrees of fineness from one another in any situation where the same is applicable.

In the following specification I will describe the new features of the invention in their application to grinding mills of the revolving hammer type, as an illustration of the principles of the invention but without intent to indicate thereby a limitation of these principles to that specific application or combination only. I

In the course of an extensive practical expe- 'rience in designing, building and operating ham- -mer mills, I have sought to enhance the efficiency of such mills by increasing the rate of discharge of ground material through the separating screen in porportion to the total area of the screen. I

have conceived that such an increased efiiciency' may'be obtained by distributing the suction effect of the air exhausting means by which a flow of air laden with ground material is induced through the separating screen, more uniformly than heretofore over all parts of the screen; and have made observations and conducted numerous experiments in studying the amount and distribution of air pressure and vacuum effects over the sepa-' rating screens in such mills. In the course of my studies on this subject I have devised the equalizing or distributing means disclosed in my prior application Serial No. 268,300, filed April '7. 1928, on which Patent No. 1,755,573 was issued April 22, 1930, and the further improvements in such means shown in this application and hereinafter described in detail.

In the drawings,

Fig. 1 is a perspective view of a grinding mill in which this invention is embodied;

Fig. 2 is a cross section on a plane transverse to the axis of the mill shown in Fig. 1;

Fig. 3 is a longitudinal section on a larger scale of the screened air-duct shown in Fig. 1;

Fig. 4 is a cross section of the duct taken online l4 of Fi 3; I

Fig. 5 is a sectional view similar to Fig. 3 showing a modification of the distributing means;

Fig. 6 is a fragmentary sectional view on line 66 of Fig. 5;

Fig. 7 is a view similar to Fig. 3 showing another modification;

Fig. 8 is a cross sectional view; and

Fig. 9 an axial view of one form or embodiment of this invention applied to a hammer mill of the common type from which the ground material is emitted through a screen surrounding the lower part of the orbit of the hammers;

Figs. 10 and 11 are views similar to Figs. 8 and 9 of another form of the same essential means applied to the same type of mill;

Figs 12 and 13 are similar views of a further modification of the same invention;

Figs. 14 and 15 are similar views of another modification applied to a mill of the same type as shown in Figs. 8:13, but of specifically difierent design.

Like reference characters designate the same parts wherever they occur in all the figures.

Referring first to Figs. 1, 2, and 3, the mill comprises a substantially cylindrical casing I having plane end walls 2 and 3, in the axial part of which is rotatably mounted a shaft- 4 which carries disks 1 ,to which hammers 5 are connected by pivot rods 6. A part of the cylindrical casing is bulged outward, as shown at l0, and in the space provided by the bulge, but outside of the orbit of the hammers and separated from the bulged wall, is a duct l2.

This duct extends from end to end of the casing. In cross section it is substantially arcuate and concentric with the shaft 4, its outer wall I! is a screen, preferably made of perforated sheet metal, its other walls are imperforate, and its ends are connected to pipes I8, 18 which join a pipe I!) leading to an exhaust fan or blower 20. Pipe I9 is subdivided into two sections, one of which has av flaring or funnel end 21, and the other of which is fitted with a sliding sleeve 22 adapted to be advanced or retracted so as to close entirely, or open to a greater or less extent, the annular space between the outer end of this sleeve and the funnel of the other pipe section. By means of this adjustment the intensity of the suction or vacuum effect caused by the fan can be regulated.

The mill is equipped with a chute through 55 which the material to be ground is admitted, and with an adjustable gate by which the volume of material delivered through the chute may be varied.

In so far as this mill corresponds with prior art mills of the same type, further description is unnecessary. It is sufficient to say, before describing the features novel with the present invention, that in operation air is constantly being exhausted from the duct I! through screen l'l by the exhaust fan, and continually being admitted through the feed .opening with the material to be ground. In their rapid rotation, the hammers strike the particles of material, breaking them by impact into smaller particles, and imparting motion to such material as well as to the air in the casing. Centrifugal force and momentum cause the ground material and air to pass through the space between the screen l1 and the bulged portion III of the casing wall, where the-ground material is subjected to the effect of air passing into the duct. This effect is greatest on the smallest particles, while centrifugal force has a greater eifect on the larger particles, causing them to pass along the outer wall and across the duct out of the influence of the air stream. These heavier particles are then struck again by the hammers and again put through the same cycle.

My experience with hammer mills has shown me that a considerable variation in the pressure or vacuum efiect exists over different parts of the screen, not only with a duct constructed and arranged as here shown, but also in mills of the type in which the air flow, centrifugal force and gravity all act in the same direction on the material adjacent to the screen. This variation affects the efliciency of the mill by causing too great concentration of the ground material at those parts of the screen where the pressure difference is greatest, with more or less clogging or liability of clogging, and utilization of less than the full discharge capacity of those parts of the screen where the pressure diiference on opposite sides is least. But with the present invention I have given to the art means for improving these conditions bymaking the pressure diflerence more zation, of the pressure effect over the screen meaning by the term equalization not necessarily that the-pressures or pressure differences are made exactly equal to one another at all points, but that there is a reasonable approach to equality, and a much closer approach to this desirable effect than has been obtained by any means heretofore used. to my knowledge, in comparable situations.

One means which I have used to obtain such equalization at different parts of the screen in the mill above described consists of partitions in the ends of the duct l2 substantially parallel to the screen I'I (by which I mean that the perpendicular distance between the partition plates and the back wall l8 of the duct, but preferably points) and nearly midway between the screen and the back wall l8 of the duct, but preferably slightly nearer the screen. Each partition extends from the end of the duct inward for about one-third of the total length of the duct. Baffles are preferably placed at the inner ends of the partition plates to effect a more distinct separation between the air currents passing through the screen to different sides of the plates. Such baflies may be mounted on the plates, or formed as integral upturned lips on their inner ends, as shown at II in Fig. 3, or they may be formed as independent strips 32, secured to the inner side of the screen, as shown in Fig. 5. Or I may combine the bailles II and 32 in the same construction. As illustrating suitable proportions for the purpose in view, but without limitation of the invention to such proportions, I may say that in a mill which I have built and operated, having a duct 15" long and about 9" .wide, with a space of 1" between the inner surfaces of the screen and back wall, I have employed partition plates 5 long at each end of the duct, separated from the inner surface of the screen and of the full width of the duct, the bailies being V in height. These baiiles may be located either inward or outward from, or in register with, the inner ends of the partitions. With this construction I have obtained a very satisfactory quality of equalization of the suction effect produced by the exhaust fan at all points in the screen.

It is seen from .Fig. 6 that the partition plates are provided with a row of holes 33 near the inner end. These holes were provided to obtain 25 a closer equalization of pressures at points on opposite sides of the baiile and closely adjacent thereto. While serving a useful purpose and therefore claimed as an element of the invention, such holes are not essential, and satisfactory results were obtained without their aid.

Where the air is exhausted from one end of the duct and the other end is closed, partitions of the character shown at 3! and 35 in Pig. 7 may be used. They divide the interior of the duct into. distinct passages and divide the total area of the screen into distinct portions or sections sub- :Iected independently to the suction effects of the several passages. A

Application of the same principles exemplified in the mill just described is illustrated in diverse forms as applied to hammer mills of the type in which the lower part of the orbit of the hammers is subtended by a screen opening into a suction chamber. Referring first to Figs. 8 and 9, the mill there shown is of a known type in which a semi-cylindrical screen 36 (of perforated sheet metal or any other suitable construction) surrounds the lower half of the rotor structure concentrically with the axis of the driving shaft.

,The outer walls 31, SI and -39 of the casing provide a vacuum -chamber into which the ground material issues from the screen, and from one end of which a duct 40 leads to an exhaust fan or equivalent apparatus. Plates 4| arranged at opposite sides of the vertical axial plane of the mill at opposite inclinations, intersect the entrance of the duct and extend toward the opposite end or side of the mill to a greater or less extent. As here shown, these plates terminate short of the opposite end, but they may extend all the way to the end. They subdivide the vacuum chamber tion of the ground material, and is caught in a final separator. Return pipes of this nature are used with many mills, and are provided with valves of suitable character to check the air flow 76 the screen, and the middle part of which crosses the exhaust duct near its horizontal diameter. This plate is short in the axial direction of the mill and illustrates the fact that the lengthwise dimension of the partition may be widely varied.

Figs. 12 and 13 show a curved U-shaped partition plate 45, the distance of which from the screen varies from end to end, being greatest at the end next to the exhaust duct. A vertical partition plate 46 leads from the middle of the partition 45 to the bottom of the exhaust chamber,

dividing in two the space within the vacuum chamber on the outer side of the U-shaped partition.

Figs. 14 and 15 show a different mill of the same type but of somewhat different design, in which the exhaust chamber is shallower and the suction duct leading therefrom is of rectangular section with greater width than height. They also show a character of partition intermediate those of Figs. 8-12, consisting of two plates 41 which are curved in their parts adjacent to the screen and are sharply bent in their lower parts 41a so as to be there perpendicular to the horizontal bottom of the suction chamber. All the forms of partition shown in Figs. 8-12 may likewise be applied to mills of the design of Figs. 14 and 15.

The herein described drawings illustrate in some measure the variety or forms in which the invention may be embodied, without being an exhaustive illustration thereof. In all instances the partitions provide separate channels, independent of one another to a greater or less extent, for air leading from separate portions or areas of the screen, whereby a better distribution of the pneumatic pressure eflect is obtained all over the area of the screen. In this way an adequate flow of air is induced throughout all parts of the screen, which are thus made available for service. to full capacity, and the efliciency ot the mill is substantially increased. It will be appreciated that the duct l2 in one form 01 the invention and the bottom part of the casing in the other forms illustrated constitute discharge hoppers, or suctionhoods, into which air carrying ground material is drawn by the exhaust or suction fan 20, and that the channels above defined may be considered as being also compartments into which such hoods or hoppers are divided by the interior partitions. The partitions likewisedivide the area of the screen into distinct suction areas substantially equal to one another.

In this specification I use the term pressure in a broad sense asincluding pressures below atmospheric and pressure differences between the atmosphere and the partial vacuum obtained by the exhausting apparatus. Wherever in an apparatus of this kind a partial vacuum or negative pressure with respect to the atmosphere is produced at one side of the screen, an equal pressure excess or positive pressure is ofcourse obtained at the opposite side of the screen. The word pressure" is used herein in the sense of this definition.

What I claim and desire to secure by Letters Patent is:

1. In a hammer mill comprising revolving hammers, a duct outside of the orbit of the hammers, one wall of which is a screen, and air exhausting means coupled. to the end of said duct,'a partition extending into the duct from the end thereof which is connected to the air exhausting means and located intermediate the screen and the opposite end of the duct, the length of said partition being a fraction only of the total length of the duct.

2. In a hammer mill comprising revolving hammers, a duct outside oi. the orbit of the hammers, one wall of which is a screen, and air exhausting means coupled to the end of said duct, 9. partition extending into the duct from the end thereof which is connected to the air exhausting means and located intermediate the screen and the opposite end of the duct, the length of said partition being a fraction only of the total length of the duct, and a baflie adjacent to the inner end of the partition projecting across the space between the partition and screen. I

3. In a hammer mill comprising revolving hammers,-a duct outside of the orbit of the hammers, one wall of which is a screen, and air exhausting means coupled to the end of said duct, a partition extending into the duct from the end thereof which is connected to the air exhausting means and located intermediate the screen and the opposite end of the duct. the length oi. said partition being a fraction only of the total length or the duct, and a baflle adjacent to the inner end of the partition projecting across the space between the partition and screen, the partition having perforations in its end portion near said baille.

WALTER J. CLEMENT. 

